This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We have raised high affinity llama single domain antibodies against GFP, and are currently endeavouring to fully characterize them. Should we be successful in this endeavor, we will be able to make generally available these important reagents in essentially unrestricted quantities.